Business, science, and entertainment applications depend upon computers to process and record data, often with large volumes of data being stored or transferred to non-volatile storage media. The non-volatile storage media typically include magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. The advantages of storing data on non-volatile storage media are numerous, including: a capability of storing hundreds of megabytes or even gigabytes of data (additional cartridges can be used to store still more data); providing a vehicle for long term storage and archival; backing up that data which resides on non-removable media; and providing a convenient vehicle for transferring data between computers. Typically, magnetic tape media is the most economical means of storing or archiving data.
The amounts of data stored, accessed and processed by computers has increased as the computing power of the internal processors has increased. Hence, storage technology is continually pushed to increase storage capacities (as well as storage reliability). Improvements in storage densities in magnetic storage media, for example, have come in many areas, including improved media materials, improved error correction techniques, and decreased bit sizes. The amount of data stored on half-inch magnetic tape, for example, has increased from megabytes of data stored on nine data tracks to gigabytes (Gbytes) of data stored on 128 tracks of data.
The improvement in data densities on magnetic storage media is due in large part to improvements made in the transducer used for reading and writing data to the magnetic storage medium. A major improvement in transducer technology has been realized with the magneto-resistive (MR) transducer developed by the IBM Corporation. The MR transducer detects magnetic field signals as resistance changes in an MR stripe. Data densities can be increased using an MR transducer because signal levels for the MR transducer are typically much higher than for conventional inductive read heads. Furthermore, the output of the MR transducer depends only on the instantaneous magnetic field from the media and is independent of media velocity or time rate of change of the sensed fields.
In a three-gap magnetic recording head, two read heads are separated by a write head; the entire distance is on the order of 1,500 to 5,000 .mu.m and can result in misalignments approaching 15 to 20 .mu.m due to tape skew. In a two-gap magnetic recording head, a single read head and a single write head are provided side-by-side photolitho-graphically, resulting in possible misalignments less than a micrometer. Consequently, the two-gap magnetic recording head can provide significant advantages over a three-gap head.
A two-gap version of a 13 Gbyte head would be a cost reduction and performance improvement over the present three-gap head. Due to track misregistration (TMR) considerations, only a two-gap head will give adequate performance. A key requirement of this type of head is the ability to servo in the same gap line which is writing with the center of read elements separated from the center of write elements by only 408 .mu.m. The present invention describes a head design which achieves very good signal-to-noise ratio (SNR) with "same-gap-servo".